1. Field of the Invention
The present invention relates to machine tool spindles. More particularly, the present invention relates to an improved machine tool quill spindle, and an adjustable quill bearing assembly for holding the machine tool quill spindle.
2. Description of Related Art
Machine tools are used extensively to mill various metal workpieces according to design specifications. Machine tools typically include a table for holding the workpiece, a cutting tool for treating the workpiece, and a rotationally mounted spindle for holding and rotating the cutting tool being used to treat the workpiece.
Generally, there are two types of machine tool spindles, the ram head spindle and the quill spindle. The ram head spindle is fixed to the machine tool head, which is a heavy metal casting. Head motion is used to move the ram head spindle parallel to the spindle centerline. The quill spindle is supported by the machine tool head, but is moved parallel to the spindle centerline relative to the head. The quill spindle consists of a rotating shaft, called the spindle, that is surrounded by a tubular housing, called the quill.
The quill spindle provides advantages over the ram head spindle. First, the quill spindle weight is significantly less than the ram head and spindle weight. Thus, the quill can accelerate at a much greater rate, and thus with less reaction force. Moreover, the quill spindle is smaller than the ram head spindle and can, therefore, project cutting tools into smaller openings. These advantages initially led to predominant use of quill spindles in the machine tool industry. However, this has not been the case in more recent years. This is because the quill spindle also suffers a major disadvantage relative to the ram head spindle. Specifically, spindle rotation speeds have increased over the years, and the increased speeds result in more heat being generated within the spindle. This heat causes the quill to expand and interfere with the quill bearings that support the quill in the head. This interference results in restrictive axial motion during the cutting process, which results in unacceptable work pieces being produced. Additionally, the spindle bearings are excessively and unevenly heated at these high rotation speeds, which places the spindle bearings under load due to uneven expansion of the bearing assemblies.
Thus, there is a need in the art for a lightweight machine tool quill spindle that remains sufficiently cool during high speed rotational motion so that unintentional restrictive axial movement of the quill spindle does not occur during the cutting process, and so that the bearings are not excessively and unevenly heated at high rotational speeds.
There is also a need in the art for a quill bearing assembly that sufficiently retains and stabilizes a machine tool quill spindle assembly within the head of a machine tool, that does not cause restrictive axial motion of the quill spindle assembly during high speed operation due to thermal expansion of the quill spindle assembly.
The present invention is a machine tool quill spindle assembly that remains cool during high speed rotational motion of the spindle. The machine tool quill spindle assembly holds machine tool cutting tools, and includes a quill assembly and a spindle assembly rotationally mounted within the quill assembly. A plurality of first coolant flow paths extend axially within and through the spindle assembly to allow a cooling fluid to circulate within and through the spindle assembly.
Another aspect of the present invention is an adjustable quill bearing for retaining and stabilizing the machine tool quill spindle assembly in a head assembly that has a generally cylindrical central bore for receiving the machine tool quill spindle assembly therein. The adjustable quill bearing includes substantially cylindrical upper and lower bearing portions. Each of these upper and lower bearing portions includes a substantially tapered elongate portion for mating with a substantially tapered elongate portion formed in upper and lower portions, respectively, of the head assembly, and a groove in an inner portion of the tapered elongate portion. A resilient, self-lubricating bearing material is mounted within each of the grooves, and provides a frictional interference fit between the head assembly and the machine tool quill spindle.